The present invention relates to a continuous production method for a monolayer powder film in which powder particles are uniformly and closely embedded in the planar direction on the surface of an adhesive layer provided on a base material in the shape of an elongated film, so that part of the powder particle protrudes, and relates to a production apparatus for a monolayer powder film which is suitable for the production method.
As a method in which powder particles are adhered to a base material, (1) an electrostatic spray method in which charged powder particles are adhered on a base material by air spraying; (2) an electrostatic flowing and soaking method in which a base material is soaked in a powder coating material fluidized by charged air and powder particles are adhered to the base material by electrostatic attraction; and (3) an electrodeposition method in which charged powder particles are dispersed into solution and are supported on a base material by applying voltage; etc., can be generally used. In addition, (4) a method in which an adhesive layer consisting of uncured resin is previously formed on the surface of a base material, and powder coating materials adhered to the surface of film forming media are embedded in the adhesive layer by using external force such as vibration, is disclosed in Japanese Unexamined Patent Publication No. 5-302176. Furthermore, (5) methods in which an adhesive layer is formed on a base material, powder particles are placed on the adhesive layer, the surface thereof is leveled by skizing, and then the powder particles are embedded in the adhesive layer by presses, pressure rollers, etc., are disclosed in Japanese Unexamined Patent Publications No. 9-318801 and No. 11-95004.
However, powder film forming methods of the above (1) to (3) are methods for adhering powder particles on the surface of a base material in multiple layers, and the methods theoretically cannot form a monolayer powder film in which powder particles are uniformly filled in the planar direction at high density. In the coating method (5), when the powder particles are adhered to and embedded in an adhesive layer consisting of uncured liquid resin, the uncured liquid resin of the adhesive layer is pushed out on the surface and then the powder particles are adhered thereto. In this case, a multiple powder layer film is surely formed, since the above process is repeated until pushing out of the uncured liquid resin is stopped. In addition, in this coating method in which the film forming media and the base material are vibrated or stirred in a container at the same time, it is difficult to apply to base materials having a large area and a high flexibility such as an elongated film, and there are problems in that the apparatus is of increased size and in that the apparatus will become contaminated by scattered powder particles.
Furthermore, although the coating method (5) can be applied to a base material in the shape of an elongated film, there were problems in that dense regions and sparse regions in powder filling density in the planar direction are easily formed, the powder particles are arranged in the flowing direction in a line, striped defects easily occur, and the like. In addition, in this method, it was also difficult to embed the powder particles to a uniform depth in the adhesive layer over the entire surface of the base material due partially to pressure differences applied from presses or pressure rollers to the film. Furthermore, with respect to the partially pressure differences, there were problems in that an adhesive layer is easily formed as a multiple layer at a place at which a large pressure is applied because other powder particles are further adhered to adhesive oozed from adhered powder particles, and in that powder particle easily coming out occurs in cleaning processes for excess powder particles at a place at which a slight pressure is applied because powder particles have not been sufficiently embedded in the adhesive layer. This phenomenon is pronounced in the case in which a large area is coated or in the case in which powder particle having an average particle diameter of 15 μm or less is used. In particular, in the case in which the average particle diameter of powder particles to be used is 15 μm or less, since the specific surface area of the powder particle is increased and the fluidity of the powder particles is substantially deteriorated by effects of electrostatic attraction due to frictional electrostatic charging, van der Waals forces, etc., it was difficult for powder particles to be adhered uniformly to the surface of the adhesive layer at high densities. Furthermore, even if there was no problem in fluidity, in such powder particles, other powder particles cannot be embedded to uniform depth in spaces between the powder particles already adhered on the adhesive layer since the pressure from pressure rollers is dispersed and the pressure applied to each powder particle is lowered.
In addition, as an apparatus for embedding the powder particles on the surface of the adhesive layer, an excitation apparatus in which a container C set on an excitation mechanism V as shown in FIG. 10, is known. The container C consists of hard materials such as hard synthetic resin, metal, etc., and is formed in a bowl shape having an opening c1 at the upper portion thereof. A column portion c3 is protrudingly provided in the center of a bottom portion c2 so as to swell and protrude above and to reach the same height as the opening c1. The excitation mechanism V is composed as follows: a vibrating plate f3 is mounted on machine stand F by way of coil springs f1 and f2; a vertical axis f4 extending above to the center portion of an upper surface of the vibrating plate f3 is protrudingly provided; a motor f5 is fixed at the center of a lower surface of the vibrating plate f3; and a heavy weight f7 is attached eccentrically to this output shaft f6 of the motor f5. The container C is mounted on the vibrating plate f3 and is set by fixing the upper edge of the column c3 on the upper edge of the vertical axis f4, and then the container C is vibrated when the motor f5 is driven and the heavy weight f7 rotates.
Powder particles and pressure media were put into the container C of this excitation apparatus, a base material on which are coated an adhesive layer and adhered powder particles was passed through the pressure medium, while the container C was vibrated. Thus, the powder particles were embedded on the surface of the adhesive layer by being struck due to the vibrating pressure media in the container C, and a powder layer was thereby formed.
However, in the above excitation apparatus, since vibration of the pressure media at the center portion in the container C differs from that at the edge portion thereof, although a monolayer powder film in which the powder particles are uniformly filled in the planar direction at a high density can be formed when the base material is small, treatment in the container C is limited when a base material has a large area and high flexibility, such as a sheet in the shape of an elongated film and there is a problem in that embedding of the powder particles is insufficient in the width direction of the base material even if the treatment is carried out.
Therefore, it is an object of the present invention to provide a continuous production method for a monolayer powder film consisting of powder particles which are closely embedded on the surface of an adhesive layer provided on a base material in the shape of an elongated film as a monolayer, so that part of the powder particle protrudes and the powder particles are closely embedded, and a production apparatus for a monolayer powder film which is suitable for the production method. A “monolayer powder” according to the present invention refers to a state in which powder particles do not overlap in the thickness direction in a plane and they are covered at about the same height and at a high density so as to contact with each other. This monolayer powder can be applied to a general coating film for esthetic enhancement and for improving durability and strength of the surface, and to a film for polishing, non-slipping or slipping, light-reflecting or anti-reflecting, insulating or conducting, light condensing or diffusing, used in a flat lens or a translucent screen, etc.